Electrostatic discharge (ESD) is known to be capable of causing catastrophic damage to microelectronic devices. Damage may include, for example, thermal damage and breakdown. Even where total failure is avoided, an ESD event may nevertheless lead to degraded performance.
The susceptibility of microelectronic devices to failure resulting from ESD events has led to the emergence of various protective features designed specifically to protect microelectronic devices from such failure. In some cases, to ensure ESD survivability of devices, ESD protection circuitry has been included with the device. This circuitry may include, for example, diode strings or other structures. Although these structures may be capable of providing the desired ESD protection to the device, they also take up valuable space on a chip, driving up cost and sometimes leading to unwanted capacitance that can degrade performance.
In certain devices such as aluminum gallium arsenide (AlGaAs)/gallium arsenide (GaAs) heterojunction bipolar transistor (HBT) devices, thick AlGaAs emitter layers have been found to provide some ESD protection. Unfortunately, however, AlGaAs emitter HBTs are also known to suffer inferior electrical characteristics, such as inferior gain versus temperature characteristics.